Aerial navigation indicator



P. R. ADAMS FAI.

AERIAL NAVIGATION INDICATOR May 24, 1960 Filed Sept. 8, 1958 May 24,1960 P. R. ADAMS ETAL 2,938,204

AERIAL NAVIGATION INDICATOR Filed Sept. 8, 1958 2 Sheets-Sheet 2Inventors ro sfnvo ,wf

PAUL R. ADAMS am AxAA/af B Ross/er I AlAR/V] .I lllilllig 0 m. 4 0R f Wn BMA .54 .ww m w. e I Mm v A 5 I :.:ia' L E I W A R A I w m 2L m 0 4Y6.3 G, R ...c nu# YNH m of fm R/cv m f ,2, Apr/ r m .IPI l y 3.3% M .m GRJa. Rvs. .kv/So 0 M n 9 .w A m I m w. R e 0 fr mm 0 A R w 3f M A aww swm/P 2? s wa o. f/w S C 3 ML 7 MW f, m L 1p. am .e .wv/m 3 M .1%7 M ,w Np .e 3 w.: 3 4I@ W .34u A E114/ n m f 2 4l l EP. V. /3 Mm f NAVIGATIONINDICATOR Paul R. Adams, Bethesda, Md., and Ben- Alexander and Robert I.Colin, Nutley, NJ., assignors to International Telephone and TelegraphCorporation, Nutley', N.J.,a corporation of Maryland Filed Sept. 8,1958, Ser. No. 759,513 v 9 Claims. (Cl. 343-102) This invention relatesto -aerial navigation system indicators and more particularly to animproved indicator system for use with a Navaglobe radio range beacon.This is a continuation in part of our copending application Serial No.382,934, led September 29, 1953 (now abandoned).

The Navaglobe radio range beacon system provides a radio beaconconsisting essentially of three transmitting antennas arranged in anequilateral triangle with means provided to successively energize theantennas in pairs Vso that different distributions of the energy areproduced in different directions about the beacon. At the beginning ofeach cycle of antenna pair energization, a synchronizing signal isprovide so that receiving means in an aircraft or other vehicle maysynchronize the signals from the antenna pairs to establish its bearingrelative to the beacon. One such beacon and receiver arrangement isshown in Patent No. 2,541,040, issued February 13, 1951, to R. I. Colin.As 'shown in the Colin patent and also as originally employed in theNava'globe system, a characteristic Navaglobe synchronizing signalconsisting of a radiated pulse or group of pulses is radiatedomnidirectionally at one cycle per second and servesto mark the start ofthe cycle of the three directional signals from the three pairs ofantennas. However, this Yuse of a synchronizing signal has been modifiedto eliminate the synchronizing pulses and a silent interval is employedto mark the start of each cycle. Thus, the radiated signals from thepairs of antennas vehicle and the silent intervals serve to synchronizea distributor control so that the successively received signals from thepairs of antennas may be utilized to indicate the crafts bearingrelative to the beacon.

In the past, the received signals were applied to different windings ofa three coil vector ratio meter whose needle assumed a positiondepending upon the vector sum o-f the fields developed in the threecoils. Although this meter performed satisfactorily it did possess somedisadvantages. For instance, considerable direct current power wasrequired to produce the magnetic field necessary to control the ratiometer needle and the needle was susceptible to external D.C, magneticiniiuence.V In addition, each meter required an individual calibrationafter installation. Furthermore, the detector system utilized a lineardetection method which incurred DLC. errors in the indicator due tonoise and this D.C. error, usually referred to as cumulative noiseerror, produced a set in the indicator that varied with the noise leveland azimuth.

One of the objects of this invention is to provide an improved Navaglobeindicator which overcomes the aforementioned disadvantages by utilizinga trigonometric coupling-device or resolverj which preferably operateswith alternating current, and a sensitive null detection deviceassociated therewith.

Another object of this invention is to utilize a square law detectionmethod in a Navaglobe indicator system to error due' noise.

are received at a4 craft or l 2,938,204 A Patented May 2.4, 1950 Itisanotherv object to employ servo mechanismswfor computing the bearingin a Navaglobe system havingfselfcontained servo loops Vwhich transformimproper settings of shaft angles directly into A.C. error voltages toenergize correcting servo motors and to providev an alarm to warn whenthe system is not in synchronization.

It is a feature ofA this ,inventionto provide a bearing indicatingsystem which` accepts the Navaglobe signals from a receiver and routesrthek information signals through vtwo different routesvto a dragV cupmotor which acts as a square -lawv device, the iirst route being to atrigonometric coupling device via a distributor which dis.- tributes thethree information signals to predetermined coils of saiddevice` andtheother route being via a v90 degree phase shifter.- Each ofthe routes arecoupled to different coilsof a drag cup motor so that the shaft outputrate of the motor represents the square of the' information signals.This shaft position output is then detected land converted toanelectrical signal by means of, for example, a Synchrotel and duringthe silent interval this electrical signal is fed to a servo motor whichdrives the rotor of the trigonometric coupling device until the outputfrom the Synchrotel, during the silent interval, is nulled. Thus, whenthe output of the Synchrotel is' nulled and the position of thetrigonometric coupling device rotor is representative of bearing..

The Synchrotel which converts the shaft output from the drag cup motorto an equivalent electrical signal is a well-known item manufactured bythe Kollsman Company and consists of a shaft position input to a tirstrotor inductivelycoupled with three stator ywindings 120 outof-phasewith each other. These windings are electrically coupled with thr'eeother stator windings also 120 out-ofphase with each other which are inturn inductively coupled with a second rotor.A 1 In the embodimenthereindescribed, this second rotor is driven by a servo. In operation,"the first rotor detects a shaft position offering very little frictionallor-other resistanceto said shaft position and the second rotor.produces an electrical signal for energizing a servo motor which,.inturn, drives the second rotoruntil itsoutput electrical signal isnulled. Thus, `whenin the null condition, the position of the secondrotor is indicative of the position of the first. rotor. The Synchrotelis particularly useful inthe embodiment hereindescribed,'although otherdevices could be substituted therefore to yield the same result. n

` The trigonometric coupling device may use, resistive inductiveorcapacitive effects. The input signals'may be applied to threeindividual members of this device and the output taken ,from a commonmember, as in the embodiment h ereindescribed, or the reverse proceduremay be used. Furthermore, either' the three individual members or thecommon member may bephysically rotated in order to produce the desiredvariations. A feature of this coupling device is that the inputNavaglobe signals whose relativey amplitudes contain theazimuth'inforrnation aresubject to the trigonometrical manipulationeffect as a 'function of the rotated memberof the device. Forillustrative purposes, inthe following description of a specificembodiment of this invention, the trigonometric coupling device isassumed to consist of a stator whose members are three coils or windingswhose axes are apart and a rotor coil inductively coupled to saidthreestator coils; the whole device being referred to asa resolver. t

Other features and objects of this invention will become more apparentby reference to the following specific description taken in conjunctionwith the accompanying drawings; in which:

' Fig. 1 illustrates the general arrangement of a Navaglobe radio beacontogether with a field pattern distribution which may be expected -forone form of Nava'globe system;

Fig. 2 is a'graphical representation of waveforms helpful in explainingthe operation of the indicator system of this invention;

Fig. 3 is a schematic diagram in block form of one embodiment of lareceiver incorporating the indicator system of this invention; and YYFig. 4 is a detailed block diagram ofthe ,commutator unit employed inFig. 3.

Referring to Fig. 1, there are represented typical field patterns whichmay be produced by antennasl, 2 and 3. Thetransmitter 4 is shown tocomprise a radio frequency transmitting source 5 and switching circuit6. Switching circuit 6 is coupled to antennas 1,2 and 3 so as toenergize this squaring action that provides square law detection to theantenna cyclically in four steps. `In the rstY step, A

none of the antennas are energized for one quarterlof ,the tcyle,effectively producing a gap or interval which may be` considered as asynchronizing signal (see Fig. 2,

curve A). Antenna pairs v1, Y2; 2, 3 and 3, lare then veach successivelyenergized by switching y,circuit 6` for Yperiods represented by pulses7, 8 and 9 of Fig. 2, curve A. When `antennas 1 and 2 are energized,preferably 'cophasally, the radiation pattern shown in dot-dash lines,atA will be produced. Successively thereafter, antennas p 3 will beenergized producing pattern Band antennas 3, l'producing pattern C.Thus, it rwill he seenY as indicatedby the scale 10 that a differenceamplitude ratio fof energies from patterns, A, B and C will be producedvabout the beacon. It will be seen that only 180 ambiguity exists. Thisambiguity can be resolved readily by ascertaining ythe geographicalposition' of the craft or may be resolved by direction finding .on twoor more beacons or other radiation points to locate generally theposition of the craft.

Referring now to Fig. 3 the improved Navaglobe indil' I cator system ofthis invention is shown wherein a receiver V11 (which is preferably ofthe super-heterodynev typebut without va detector) and which may bemounted on any mobile craft or other location at which it is desired toascertain the azimuthal position relative to the beacon,

receives from Iantenna 12 some of the energy radiated by the beaconshown in Fig. l. Receiver 11 is preferably tunable to differenttransmitting stations and yields an IF output signal preferably at1500cycles. Thus, the

[output energy from receiver 11-is simply the undetected IF which hasthe forms shown at Bin Fig.2 and corisists of an IF waveof 1500 cyclesmodulated `.by the characteristic Navaglobe keying cycle yshown inFig.2, curve A. This output from the receiver is applied via .a

preamplifier 13 to AGC circuit 14, which in turn, controls the -gain ofreceiver 11. This automatic gain circuit is extremely slow acting in order not to'disturb the amplitucle ratio of the three Navaglobe signalswithin anyone cycle. .Another output .from preamplifier 13 is fed tocoil 15'. of drag cup motor 16 via 90 phase shifter 17 and amplifier 18While a third output from preamplifier 13 is fed to synchronizedcommutator device 19.

The purpose of synchronized. commutator 19 is to -feed reach of thethree Navaglobe signals Within a vcycle to a v different one of thestator coils 20, 21 or 22 of trigonometric resolver 23. Since thefthreesignals are sequential. as shown in the waveforms of Fig. 2, rotor coil24 of resolver 23 will be sequentially energized by the three signalswithin a cycle. The signal'induced in rotor coil 24 is fred to statorcoil 25 of drag cupY motor 16 via amplifier 26. Thus, the two statorcoils 15 andy 25 of drag cup motor 16 are simultaneously energized bythe same Navaglobe signal, except that the signalfed to coil 1S isshifted 90 in phase relative to the signal fed Vto coil 25. When bothstator coils of drag cup motor 16 are energized, the torque on' theoutput shaft of the motor is the product of the energizing signal; jConsequently, in the embodiment of this invention hereindescribed, thistorque is the square of the Navaglobe signals additionally rmultipliedby the sign of the.` roto1 angle of Aresolver 23 duetothe transformationaction of the' resolver. It is The shaft output from drag cup motor 16is applied Yto Synchrotel 27. This Synchrotel unit is a brushless, lowinertiav control transformer usually employed totransmit'electricalsignals `representing the difference between twoinput motions. The Synchrotel is manufactured by the Kollsman Companyand is described in their catalog ynumber M'-9`0-1000-l15'.v It has tworotors andY two sets of ,stator coils with corresponding coils on eachset of stator coils being coupled together and 1s here 'employed inconjunction with a servo motor energized byY thesignal induced in one.of the rotors to drive the same rotor. The input rotation totheSynchrotel which is followed by the action of the servo motor, isapplied to 'the brushless, low inertia rotor of the SynchroteLV'Thus,'.in this invention, as shown in Fig. 3, the shaft outputfrom'the drag cup motor is -applied to the low inertia rotor of theSynchrcrtel 27 and the other rotor of the, Synchrotel is driven by aservo motorr28 which lis responsive to the signal output from that sameother rotor via a switch in synchronized commutator 19, switch 29 andservo amplifier 30. Y

l Servo motorY 28 also drives bearing indicator 31 and rotor coil 2,4 oftrigonometric resolver 23.V Thus, atwofold action is performed by servomotor 28. -The first is yto null the electrical output from fSynchrotel27 by positioning a rotor ofthe Synchrotel to follow the shaft Youtputof drag cup motor ,16 during the silent interval. The other function isto position rotor coil 24 vof resolver 23, during the silent interval,so that the three 'signals sequentially induced in rotor coil 24 by theNavaglobe signals appiledY to stator coils 20, 21 and 22 of resolver-23,will sum up to zeroV over the cycle. When this occurs it is evident thatthe three rotations of Vthe shaft output-of drag cup motor 16 during thesame Navaglobe cycle will add up to zero, provided bearing to 'theNavaglobe beacon has not changed. Thus, bysensing the Synchrotelelectrical output during the silentY interval following the Navaglobecycle and driv- `ing both the Synchrotel 27 and the resolver 23 to nullthe output of Nthe Synchrotel during that silent interval, the shaftpositions of the drag cup motor, the Synchrotel, the resolver Vand theservo motor will 'all represent the relative bearing from the antenna 12'to the Navaglobe beacon. VSwitch 29 and left-right deviation indicator32 are provided for operating the system to indi- Vvcate. deviation froma preset bearing. For'example, the position vof rotor coil 24. is set ata desired bearing and switch 29 is set at itsterminal 29h, whereupon thesignal .from Synchrotel'27 during the silent interval energizes vput ofpreamplifier 13 shown in Fig. 2, curve C. -The purpose of filter V33 isto detect the four-cycle signal component of thetransmitted'energy fromthe beacon producing a four-cycle sine wave suchas shown in Fig. 2,curve D.Y This four-cycle sine VWave is then fed to shaper` 34 'whichshapes it into a positive swinging squarewave for energizing steppingswitch drive 35. Inhibit circuit 36 isinsertedbetween sh'aper 34anddrive 35 sothatipulses from the shaper may be preventedfromenergizing the switch drive causing it to skip as is required to.achieve synchronization. Switch drive 35 drives two Vsets of rotaryswitches37 and 38. 'When the system is in synchroniza`- rg tion theoutput from preamplifier 13 consisting of the three Navaglobe signals at1500 cycles is coupled to the rotating arm of switch 37 and fed to threeterminals of said switch which are coupled to the three coils 20, 21 and22 of trigonometric resolver 23. The fourth terminal of switch 37 iscoupled to the input of monostable multiy vibrator 39. When insynchronization, this fourth terminal detects the silent interval andthus provides no signal to multivibrator 39, however, when not insnychronization, this fourth terminal detects one of the three Navaglobesignals and, thus, triggers the multivibrator. Each time it is triggeredmultivibrator 39 provides an output signal of sufficient duration toblock the next square wave pulse from Shaper 34 so that switch drive 35skips a step. This process continues until the silent interval arriveswhen switch 37 is on its fourth terminal and the system is insynchronization. A second rotary switch 38 is provided to feed theelectrical output from Synchrotel 27 to servo amplifier 30 during thesilent interval and alarm 40 which is coupled to the fourth terminal ofswitch 37 is energized whenever the system is not in synchronization.Alarm 40 may be any sort of audible or visual alarm having a period ofabout one second following an energization signal.

Referring to Fig. 2 there is shown the various waveforms helpful inunderstanding this invention. The intermediate frequency output fromreceiver 11 comprising a 1500 c.p,s. voltage modulated by thecharacteristic Navaglobe keying cycle is shown in Fig. 2, curve B, andis applied to preamplifier 13 whose output is directed into twochannels. The first output is directed to drag cup motor 16 via phaseshifter 17 and the second is put through high Q four-cycle filteramplier 33. The high Q of filter 33 enables the silent interval to coastthrough so that the output of the lter is essentially a four-cycle persecond sine wave as shown in Fig. 2, curve D. This output is thenapplied to shaping circuit 34 which has its operating point so selectedthat the four-cycle filter output voltage will drive it from fullconduction to a non-conducting condition resulting in a square waveoutput. Rotary ystepping switch drive 35 and rotary switches 37 and 38may be forward acting rotary stepping switches of the type commonlyemployed in telephone switching circuits and respond quite readily toenergizations occurring at a rate at four-times a second.

As mentioned hereinabove, there is no action of the bearing measuringsystem when the rotor angle of trigonometric resolver 23 is set properlyand consequently there is no net motion of the drag cup motor rotor asmeasured during the silent interval. However, if the rotor angle of theresolver 23 is not set properly, then there will be a net motion of thedrag cup rotor and this net motion sensed during the silent intervalwill drift causing `servo motor 28 to drive during each silent intervaluntil the rotor angle of resolver 23 is set properly. For example, ifthe rotor of resolver 23 is set ofi to the right then the drag cup rotorwill also drift towards the right in its net motion and if the rotorangle of the resolver is set improperly to the left, then the net motionof the drag cup motor rotor will be adrift towards the left. In otherwords, the drag cup motor stores sequential signals in the form ofrotations yielding the sum of these signals during the silent intervaland the net motion of the drag cup motor representative of this sum is adetector of the improper or proper setting of the resolver rotor. Thedrag cup motor is used merely as a servo detector to provide errorvoltage when the resolver rotor is not set properly. As also mentionedhereinabove the drag cup motor is an electromechanical device whosetorque is propo-rtional to the product of currents flowing in its statorWindings. It is filled with a silicon damping fluid and hence it rotatesslowly during the application of voltages to its field coils. One suchdrag cup motor is manufactured by Clifton Precision Products Corporationof Philadelphia, Pennsylvania.

While We have describedabove the principles of our invention inconnection with specific apparatus, itis tobe clearly understood thatthis 'description is made only by way of example and not as a limitationto the scope of our invention as set forth in the objects yandaccompanying claims.

l. In a radio beacon system having a beacon with cyclinically andsuccessively transmitted signals in a plurality of differently directedradiation patterns and a synchronizing signal, an indicating receivercomprising'means for sensing said synchronizing signal, atrigonometrical coupling devicehaving stator and rotor members, meansfor coupling energy defining said different radiation patterns to saidcoupling device, means under control of said sensing means for selectingenergy from said v'coupling device in accordancevwith the timing of saiddifferent radiation patterns, the summation null of the outputs of Isaidcoupling device being determined by the position of `said rotor member,a null sensing device and means to Ysensing said synchronizing interval,a trigonometrical coupling device having stator and rotor members, meansfor coupling energy defining different radiation patterns to saidcoupling device, means under control of said sensing means for providingenergy from said coupling device in accordance with the timing of saiddifferent radiationv patterns, the summation null of the outputs of saidcoupling device being determined by the position of said rotor member, ameter to indicate said rotor position and means to rotate the rotormember of said coupling device, a null sensing device and means tocouple the outputs of said coupling device to said null sensing devicewhereby the null indication of said sensing device is indicative of therotor position represented by said meter which represents the bearing ofsaid receiver with respect to said beacon.

3. A radio beacon system having a beacon which cyclically andsuccessively transmits signals in a plurality of differently directedradiation patterns and a synchronizing interval, an indicating receivercomprising means for detecting said radiation, a trigonometricalcoupling device having a rotor and stator members, synchronizing meanscoupling said detector to said coupling device, means to square theoutput of said coupling device and store signals therefrom during acycle, motor means for driving said rotor member, sensing means couplingthe output of said squaring and storage means to `said motor meansduring said synchronizing interval whereby said motor means is energizedto drive the rotor of said trigonometrical coupling device until a nullis produced at the output of said sensing means.

4. In a radio beacon system having a beacon which cyclically andsuccessively transmits signals .in a plurality l of differently directedradiation patterns following a synchronizing interval, a bearingindicating receiver comprising means for detecting said radiations, atrigonometrical coupling device, synchronizing means coupled to theoutput of said receiver for applying signals representing each of saidradiation patterns to elements of said coupling device, signal squaringand storage means coupled to the output of said trigonometrical couplingdevice and also to the output of said receiver, motor means forpositioning said coupling device, comparing means coupled to the outputof said squaring and storage means and also coupled to the output ofsaid motor drive means for comparingthe output of said squaring andstorage means with said motor means output and producing a signal forenergizing said motor means during said synchronizing interval so thatsaid motor means is energized during said interval .driving saidtrigonometrical coupling device Vto :a position representative ofbearing. 5. In a radio beacon system having .a beacon which cyclicallyand successively transmits signals in a plurality of differentlydirected radiation patterns and a synchronizing-interval, an indicatingreceivercomprising means for sensing said differently directed signalsin saidvsynchronizing interval, a trigonometrical coupling device, asynchronized commutator devicercoupling said receiver to saidtrignometrical coupling device having lrotor and stator members, motormeans for driving said rotor member, signal storage means coupled tosaid receiver and to the output of said rotor member and switching meanscoupling the output of said storage means to saidmotor so that saidmotor drives said rotor member to nullrthe output from said storagemeansand bearing indicating means coupled to the output of said motormeans. jY

6. A radio beacon system andY receiver indicator for indicating abearing of said receiverfrelative tovsaid beacon comprising abeaconwhich cyclically andA successively transmits signals in aplurality of differently directed radiation patterns followed by asynchronizingV interval, an antenna -for detecting said radiations, areceiver coupled to said antenna, a resolver comprising stator membersand a rotor member, a sychronized commutator coupling the output of saidreceiver to said stator members, a drag cup motor having two statormembers anda rotor member, phase shifting means coupling the output 'ofsaid receiver to one of said drag cup stator members, means couplingthe'output of the rotor member of said resolver to another'V drag cupstator member, a low inertia control transformenj driven by said dragcup motor and said motor drive means producing/an error signal andYsyncbronized switching means coupling said error signals to said motordrive means during saidY synchronizing intervalvsor that said resolverrotor is driven to a position representative of bearing.

7. A system as in claim 6, and further including Yselector means forfixing the position of said motor drive and said resolver rotor andsupplying said error signal to a null indicator to indicate deviationsfrom thebearing represented byV the iixedY position of said motorYdrive.'-

8. A- system as in claim 6, wherein said synchronized commutatorincludes lter means coupled to the output of said receiver producing asine wave at the fundamental frequency of the radiations from saidbeacon, signal shaping means coupled to the output of said filter, arotary stepping switch, gating means coupling the output of said Shaperto said rotary stepping switch, means coupling the output of saidreceiver to the'rst rotating arm of said stepping switch, vmeanscoupling said error signal to the second rotating arm of said steppingswitch, meansV coupling predetermined `terminals associated with saidiirst rotating arm to statorv members of said resolverya multivibratormeans coupling another of said rst terminals to said multivibratorsupplying a control signal to saidgate, and means coupling apredetermined one of saidsecond set of terminals to said motor drivemeans.

9.,A system as in claim 8, further including alarm meanscoupled to theinput -of said multivibrator.

No references cited.

